LM3561TMX/NOPB

LM3561 www.ti.com SNOSB44C – MARCH 2011 – REVISED MAY 2013 Synchronous Boost Converter With 600-mA High-Side LED Driver and I2C-Compatible Interface Check for Samples: LM3561 FEATURES 1 • 2 • • • • • • • • • • • • High-Side Current Source Allows Grounded LED Cathode Up to 90% Efficient Ultra-Small Solution Size: VIN) the inductor will typically be the biggest area of efficiency loss in the circuit. Therefore, choosing an inductor with the lowest possible series resistance is important. Additionally, the saturation rating of the inductor should be greater than the maximum operating peak current of the LM3561. This prevents excess efficiency loss that can occur with inductors that operate in saturation. For proper inductor operation and circuit performance ensure that the inductor saturation and the peak current limit setting of the LM3561 is greater than IPEAK. This can be calculated by: 28 Submit Documentation Feedback Copyright © 2011–2013, Texas Instruments Incorporated Product Folder Links: LM3561 LM3561 www.ti.com IPEAK = SNOSB44C – MARCH 2011 – REVISED MAY 2013 I LOAD VOUT V x (VOUT - VIN) x + 'IL where 'IL = IN K VIN 2 x f SW x L x VOUT (3) ƒSW = 2MHz, and η can be found in the Typical Performance Characteristics plots. Table 15. Recommended Inductors Manufacturer L Part Number Dimensions (L×W×H) RDC ISAT Coilcraft 1µH XPL2010-102ML 2mm×1.9mm×1mm 81mΩ 1.6A TDK 1µH VLS252012T-1R0N 2mm×2.5mm×1.2mm 73mΩ 2.7A TDK 1µH VLS2010-1R0N 2mm x 2mm x 1mm 90mΩ 1.65A TDK 1µH VLS2012ET-1R0N 2mm x 2mm x 1.2mm 71mΩ 1.65A TDK 1µH VLS20160ET-1R0N 2mm x 1.6mm x 0.95mm 100mΩ 1.5A TDK 1µH VLS252010ET-1R0N 2.5mm x 2mm x 1mm 70mΩ 1.9A NTC THERMISTOR SELECTION Programming bit [4] of Configuration Register 1 with a (1) selects Thermal Comparator mode, making the LEDI/NTC pin a comparator input for flash LED thermal sensing. The thermal sensing circuit consists of a negative temperature coefficient (NTC) thermistor and a series resistor which forms a resistive divider (see Figure 38). VIN IN SW OUT LM3561 VBIAS NTC SDA RBIAS LED SCL R(T) GND Low Thermal Resistance Between LED and R(T) Figure 38. NTC Circuit The NTC thermistor senses the LEDs temperature via conducting the LEDs heat into the NTC thermistor. Heat conduction is improved with a galvanic connection at GND (LED cathode and NTC thermistor GND terminal) and by placing the thermistor in very close proximity to the flash LED. NTC thermistors have a temperature to resistance relationship of: E R(T) = R25°C x e § 1 - 1· ©T °C+ 273 298¹ (4) where β is given in the thermistor datasheet and R25C is the thermistor's value at +25°C. RBIAS is chosen so that it is equal to: R BIAS = RT( TRIP) (VBIAS - VTRIP ) VTRIP (5) Submit Documentation Feedback Copyright © 2011–2013, Texas Instruments Incorporated Product Folder Links: LM3561 29 LM3561 SNOSB44C – MARCH 2011 – REVISED MAY 2013 www.ti.com where R(T)TRIP is the thermistor's value at the temperature trip point, VBIAS is the bias voltage for the thermistor circuit, and VTRIP = 1V (typical). Choosing RBIAS here gives a more linear response around the temperature trip voltage. For example with VBIAS = 1.8V and a thermistor whose nominal value at +25°C is 10kΩ and a β = 3380K, the trip point is chosen to be +93°C. The value of R(T) at 93°C is: RBIAS is then: º » ¼ R(T) = 10 k : x e E º 1 - 1 93 + 273 298 »¼ = 1.215 k: 1.215 k: x (1.8 V - 1V) = 972: 1V (6) Figure 39 shows the linearity of the thermistor resistive divider of the previous example. 2 1.8 1.6 VLED/NTC (V) 1.4 1.2 1 0.8 0.6 0.4 0.2 0 30 60 50 60 70 80 90 100 Temperature (°C) Figure 39. Thermistor Resistive Divider Response vs Temperature VLEDI/NTC vs Temp (VBIAS = 1.8V, THERMISTOR = 10kΩ at +25C, β = 3380, RBIAS =972Ω) Another useful equation for the thermistor resistive divider is developed by combining the equations for RBIAS, and R(T) and solving for temperature. This gives the following relationship. E x 298 °C - 273°C T( °C) = VTRIP x RBIAS ª º E 298°C x LN «(VBIAS - VTRIP ) x R25 °C» + ¬ ¼ (7) Using a spreadsheet such as Excel, different curves for the temperature trip point T(°C) can be created vs RBIAS, Beta, or VBIAS in order to help better choose the thermal components for practical values of thermistors, series resistors (R3), or reference voltages VBIAS. NTC THERMISTOR PLACEMENT The termination of the thermistor must be done directly to the cathode of the Flash LED in order to adequately couple the heat from the LED into the thermistor. Consequentially, the noisy environment generated from the switching of the LM3561's boost converter can introduce noise from GND into the thermistor sensing input. To filter out this noise it is necessary to place a 0.1µF or larger ceramic capacitor close to the LEDI/NTC pin. The filter capacitor's return must also connect with a low-impedance trace, as close as possible to the GND pin of the LM3561. 30 Submit Documentation Feedback Copyright © 2011–2013, Texas Instruments Incorporated Product Folder Links: LM3561 LM3561 www.ti.com SNOSB44C – MARCH 2011 – REVISED MAY 2013 Layout Recommendations The high frequency and relatively large switching currents of the LM3561 make the choice of layout important. The following steps should be used as a reference to ensure the device is stable and maintains proper voltage and current regulation across its intended operating voltage and current range. 1. Place CIN on the top layer (same layer as the LM3561) and as close to the device as possible. The input capacitor conducts the driver currents during the low-side MOSFET turn-on and turn-off and can see current spikes over 500mA in amplitude. Connecting the input capacitor through short wide traces on both the IN and GND terminals will reduce the inductive voltage spikes that occur during switching and which can corrupt the VIN line. 2. Place COUT on the top layer (same layer as the LM3561) and as close as possible to the OUT and GND terminal. The returns for both CIN and COUT should come together at one point, and as close to the GND pin as possible. Connecting COUT through short wide traces will reduce the series inductance on the OUT and GND terminals that can corrupt the VOUT and GND line and cause excessive noise in the device and surrounding circuitry. 3. Connect the inductor on the top layer close to the SW pin. There should be a low-impedance connection from the inductor to SW due to the large DC inductor current, and at the same time the area occupied by the SW node should be small so as to reduce the capacitive coupling of the fast dV/dt present at SW that can couple into nearby traces. 4. Avoid routing logic traces near the SW node so as to avoid any capacitively coupled voltages from SW onto any high impedance logic lines such as TX1/TORCH/GPIO1, TX2/GPIO2/INT, HWEN, LEDI/NTC (NTC mode), SDA, and SCL. A good approach is to insert an inner layer GND plane underneath the SW node and between any nearby routed traces. This creates a shield from the electric field generated at SW. 5. Terminate the Flash LED cathode directly to the GND pin of the LM3561. If possible, route the LED return with a dedicated path so as to keep the high amplitude LED current out of the GND plane. For a Flash LED that is routed relatively far away from the LM3561, a good approach is to sandwich the forward and return current paths over the top of each other on two adjacent layers. This will help in reducing the inductance of the LED current paths. 6. The NTC Thermistor is intended to have its return path connected to the LED's cathode. This allows the thermistor resistive divider voltage (VNTC) to trip the comparators threshold as VNTC is falling. Additionally, the thermistor to LED cathode junction can have low thermal resistivity since both the LED and the thermistor are electrically connected at GND. The draw back is that the thermistor's return will see the switching currents from the LM3561's boost converter. Because of this, it is necessary to have a filter capacitor at the NTC pin which terminates close to the GND of the LM3561 and which can conduct the switched currents to GND. Submit Documentation Feedback Copyright © 2011–2013, Texas Instruments Incorporated Product Folder Links: LM3561 31 LM3561 SNOSB44C – MARCH 2011 – REVISED MAY 2013 www.ti.com REVISION HISTORY Changes from Revision B (April 2013) to Revision C • 32 Page Changed layout of National Data Sheet to TI format .......................................................................................................... 31 Submit Documentation Feedback Copyright © 2011–2013, Texas Instruments Incorporated Product Folder Links: LM3561 PACKAGE OPTION ADDENDUM www.ti.com 10-Dec-2020 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan (2) Lead finish/ Ball material MSL Peak Temp Op Temp (°C) Device Marking (3) (4/5) (6) LM3561TME/NOPB ACTIVE DSBGA YFQ 12 250 RoHS & Green SNAGCU Level-1-260C-UNLIM -40 to 85 DV LM3561TMX/NOPB ACTIVE DSBGA YFQ 12 3000 RoHS & Green SNAGCU Level-1-260C-UNLIM -40 to 85 DV (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of